chore: upgrade tooling stack

- TypeScript 3.9 -> 5.8
- ESLint 6 -> 9 (flat config)
- Prettier 1 -> 3
- eslint-plugin-vue 6 -> 9
- Add vue-tsc for type checking
- Migrate Sass @import to @use syntax
- Fix Pinia persistence config for v4
- Add Spotify type declarations
- Remove unused registerServiceWorker.ts

eslint.config.js

@@ -0,0 +1,33 @@
+import js from '@eslint/js'
+import pluginVue from 'eslint-plugin-vue'
+import tseslint from 'typescript-eslint'
+import eslintConfigPrettier from 'eslint-config-prettier'
+
+export default tseslint.config(
+  {
+    ignores: ['dist/**', 'node_modules/**', '*.config.js', '*.config.ts']
+  },
+  js.configs.recommended,
+  ...tseslint.configs.recommended,
+  ...pluginVue.configs['flat/essential'],
+  {
+    files: ['**/*.vue'],
+    languageOptions: {
+      parserOptions: {
+        parser: tseslint.parser
+      }
+    }
+  },
+  {
+    rules: {
+      '@typescript-eslint/no-unused-vars': 'warn',
+      '@typescript-eslint/no-unused-expressions': 'off',
+      '@typescript-eslint/no-explicit-any': 'warn',
+      '@typescript-eslint/no-empty-object-type': 'off',
+      'vue/multi-word-component-names': 'off',
+      'no-console': process.env.NODE_ENV === 'production' ? 'warn' : 'off',
+      'no-debugger': process.env.NODE_ENV === 'production' ? 'warn' : 'off'
+    }
+  },
+  eslintConfigPrettier
+)